Effect of CD34 cell dose on hematopoietic reconstitution and outcome in 508 patients with multiple myeloma undergoing autologous peripheral blood stem cell transplantation

Background: We analyzed the hematopoietic reconstitution and outcome of 508 patients with multiple myeloma (MM) with respect to the number of CD34 + cells reinfused at our center. Patients and methods: Each cohort of 390 patients (unselected CD34+ cell transplant) and 118 patients (CD34+ selected transplant) was divided into four subgroups. Among the 390 transplantations, 86 patients received a high dose (HD-) of ¡Ý6.50 ¡Á 106 unselected CD34+ cells/kg, 116 patients a low dose (LD-) of <3.00 ¡Á 106 CD34+ cells/kg. Among the patients treated with CD34+ selected PBSC, 34 received ¡Ý6.50 ¡Á 106 CD34+ cells/kg (HD+) and 16 <3.00 ¡Á 106 CD34 + cells/kg (LD+). Results: HD- patients experienced a reduced median time to leukocyte (13 d vs. 14 d) (P < 0.001) and platelet reconstitution >20 ¡Á 109/L (10 d vs. 12 d) (P < 0.001). Similarly, HD+ showed a reduced median time to leukocyte (12 d vs. 15 d) (P < 0.001) and platelet recovery >20 ¡Á 10 9/L (10 d vs. 11 d) (P = 0.058). CD34+ cell-dose was significant for long-term platelet recovery at day 360 (unselected transplant P = 0.015, selected transplant P = 0.023). Number of transplanted CD34+ cells had no significant impact on transplant related mortality, overall survival or CR/PR rates within 100 d. In terms of supportive care the differences of high-/low-dose grafts were minimal. Conclusions: These results confirm that high doses of CD34+ PBSC shorten hematopoietic reconstitution and reduce hospitalization. Nevertheless secure engraftment results from transplantation of 2.00-3.00 ¡Á 106 CD34 + cells/kg. As 60% of our pretreated patients are able to collect ¡Ý5.00 ¡Á 106 CD34+ cells/kg within a single leukapheresis, division into two or more freezing bags allows safe tandem transplantation in the majority of MM patients.